Already, there are as many as 250 service members in the process of transitioning to their preferred genders or who have been approved to formally change gender within the Pentagon’s personnel system, according to several defence officials.

The Pentagon has refused to release any data on the number of transgender troops currently serving. A RAND study found that there are between 2,500 and 7,000 transgender service members in the active duty military, and another 1,500 to 4,000 in the reserves.

Transgender service members have been able to serve openly in the military since last year, when former Defence Secretary Ash Carter ended the ban. Since Oct. 1, transgender troops have been able to receive medical care and start formally changing their gender identifications in the Pentagon’s personnel system.

But Carter also gave the services until July 1 to develop policies to allow people already identifying as transgender to newly join the military, if they meet physical, medical and other standards, and have been stable in their identified genders for 18 months. Military chiefs recently announced a delay on allowing transgender people from enlisting.

Key concerns include whether currently enlisted troops have had medical or other issues that cause delays or problems with their ability to deploy or meet physical or other standards for their jobs. Military leaders also wanted to review how transgender troops are treated, if they’re discriminated against or if they have had disciplinary problems, the officials said. They were not authorized to discuss internal deliberations publicly so spoke on condition of anonymity.